How to encode coordinate reference system definitions. Builds on
referenceSystems.xsd to encode the data needed to define coordinate reference systems,
including the specific subtypes of coordinate reference systems.
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This schema encodes the Coordinate Reference System (SC_) package of the extended UML Model
for OGC Abstract Specification Topic 2: Spatial Referencing by Coordinates, with the exception
of the abstract "SC_CRS" class. The "SC_CRS" class is encoded in referenceSystems.xsd, to
eliminate the (circular) references from coordinateOperations.xsd to
coordinateReferenceSystems.xsd. That UML model is adapted from ISO 19111 - Spatial referencing
by coordinates, as described in Annex C of Topic 2.
Caution: The CRS package in GML 3.1 and GML 3.1.1 is preliminary, and is expected to undergo
some modifications that are not backward compatible during the development of GML 3.2 (ISO
19136). The GML 3.2 package will implement the model described in the revised version of ISO
19111.
A coordinate reference system consists of an ordered sequence of coordinate
system axes that are related to the earth through a datum. A coordinate reference system is
defined by one datum and by one coordinate system. Most coordinate reference system do not
move relative to the earth, except for engineering coordinate reference systems defined on
moving platforms such as cars, ships, aircraft, and spacecraft. For further information, see
OGC Abstract Specification Topic 2.
Coordinate reference systems are commonly divided into sub-types. The common classification
criterion for sub-typing of coordinate reference systems is the way in which they deal with
earth curvature. This has a direct effect on the portion of the earth's surface that can be
covered by that type of CRS with an acceptable degree of error. The exception to the rule is
the subtype "Temporal" which has been added by analogy.
Association to a coordinate reference system, either referencing or containing
the definition of that reference system.
A coordinate reference system describing the position of points through two or
more independent coordinate reference systems.
Ordered sequence of associations to all the component coordinate
reference systems included in this compound coordinate reference system.
An association to a component coordinate reference system included in this
compound coordinate reference system.
Association to a compound coordinate reference system, either referencing or
containing the definition of that reference system.
A coordinate reference system based on an ellipsoidal approximation of the
geoid; this provides an accurate representation of the geometry of geographic features for a
large portion of the earth's surface.
Association to the ellipsoidal coordinate system used by this CRS.
Association to the geodetic datum used by this CRS.
Association to a geographic coordinate reference system, either referencing or
containing the definition of that reference system.
A 1D coordinate reference system used for recording heights or depths. Vertical
CRSs make use of the direction of gravity to define the concept of height or depth, but the
relationship with gravity may not be straightforward. By implication, ellipsoidal heights
(h) cannot be captured in a vertical coordinate reference system. Ellipsoidal heights cannot
exist independently, but only as an inseparable part of a 3D coordinate tuple defined in a
geographic 3D coordinate reference system.
Association to the vertical coordinate system used by this CRS.
Association to the vertical datum used by this CRS.
Association to a vertical coordinate reference system, either referencing or
containing the definition of that reference system.
A 3D coordinate reference system with the origin at the approximate centre of
mass of the earth. A geocentric CRS deals with the earth's curvature by taking a 3D spatial
view, which obviates the need to model the earth's curvature.
Association to the Cartesian coordinate system used by this CRS.
Association to the spherical coordinate system used by this CRS.
Association to a geocentric coordinate reference system, either referencing or
containing the definition of that reference system.
A coordinate reference system that is defined by its coordinate conversion from
another coordinate reference system (not by a datum). This abstract complexType shall not be
used, extended, or restricted, in an Application Schema, to define a concrete subtype with a
meaning equivalent to a concrete subtype specified in this document.
Association to the coordinate reference system used by this derived CRS.
Association to the coordinate conversion used to define this derived CRS.
A 2D coordinate reference system used to approximate the shape of the earth on
a planar surface, but in such a way that the distortion that is inherent to the
approximation is carefully controlled and known. Distortion correction is commonly applied
to calculated bearings and distances to produce values that are a close match to actual
field values.
Association to a projected coordinate reference system, either referencing or
containing the definition of that reference system.
A coordinate reference system that is defined by its coordinate conversion from
another coordinate reference system but is not a projected coordinate reference system. This
category includes coordinate reference systems derived from a projected coordinate reference
system.
Type of a derived coordinate reference system.
Reference to a source of information specifying the values and meanings
of all the allowed string values for this DerivedCRSTypeType.
Association to the coordinate system used by this CRS.
Association to a non-projected derived coordinate reference system, either
referencing or containing the definition of that reference system.
A contextually local coordinate reference system; which can be divided into two
broad categories:
- earth-fixed systems applied to engineering activities on or near the surface of the earth;
- CRSs on moving platforms such as road vehicles, vessels, aircraft, or spacecraft.
For further information, see OGC Abstract Specification Topic 2.
Association to the engineering datum used by this CRS.
Association to an engineering coordinate reference system, either referencing
or containing the definition of that reference system.
An engineering coordinate reference system applied to locations in images.
Image coordinate reference systems are treated as a separate sub-type because a separate
user community exists for images with its own terms of reference.
Association to the oblique Cartesian coordinate system used by this CRS.
Association to the image datum used by this CRS.
Association to an image coordinate reference system, either referencing or
containing the definition of that reference system.
A 1D coordinate reference system used for the recording of time.
Association to the temporal coordinate system used by this CRS.
Association to the temporal datum used by this CRS.
Association to a temporal coordinate reference system, either referencing or
containing the definition of that reference system.